After 2 years, the risk for these men dropped only slightly, making them 14 times more likely to be reinfected.
The results of a 5-year study have shown that men who are infected with one type of genital human papillomavirus (HPV) were 20 times more likely to be reinfected with the same type in 1 year, and 14 times more likely to be reinfected in 2 years, suggesting that the body does not build a natural immunity to HPV.
According to the Centers for Disease Control and Prevention (CDC), about 1 in 4 individuals in the United States is infected with HPV, making it the most common sexually transmitted infection. There are more than 150 types of HPV, and although most are linked with genital warts of the mouth and throat, a handful of types have been directly linked with some cancers. Indeed, each year in the United States, some 31,000 men and women are diagnosed with a cancer that was caused by an HPV infection.
The vaccines that currently exist protect against between 4 and 9 of the most common strains, including those that have been linked with cancer, and therefore, the CDC stresses the importance of encouraging all “11 to 12 year olds to get 2 doses of HPV vaccine—rather than the previously recommended 3 doses—to protect against cancers caused by HPV. The second dose should be given 6-12 months after the first dose.”
Despite the availability of the vaccines, full uptake of the 2-dose regimen remains at 43%. Meanwhile, the incidence of HPV continues to increase and recent reports have revealed that 1 in 9 men in the United States is infected with oral HPV. According to Ashish A. Deshmukh, PhD, MPH, assistant professor at the University of Florida’s College of Public Health and Health Professions, who was the senior author on the study that revealed this startling information, “One suspects that the HPV persists longer (doesn’t clear easily) among men, and that might be causing increased prevalence. It is also possible that men acquire oral HPV more readily than women.” He admitted, however, that more research was needed to pinpoint the exact reason behind this finding.
This additional research may come in the form of the 5-year study.
For the analysis, investigators from the University of Chicago Medical Center set out to determine why so many different types of HPV were coexisting together. The investigators “analyzed data regarding the spread of the disease from the ‘HPV in Men study’, which tracked more than 4000 unvaccinated men from 3 cities in Florida, Mexico and Brazil over 5 years from 2005 to 2009,” according to a press release on the study.
The results of the study showed that those men who were infected with HPV16, which is the strain responsible for most of the HPV-related cancers, had a risk of reinfection after 1 year that was 20 times higher (than an individual acquiring the virus for the first time). That risk remained relatively high at 2 years as well, at 14 times greater.
Interestingly, a man’s sexual activity during that time did not make a difference; the effect was seen in both sexually-active and celibate men. The investigators state that this suggests that the men, “are not reacquiring the virus from another sexual partner.”
As indicated in the press release on the study, “Usually, diversity of so many types of viruses happens as they compete to evolve different ways to evade the immune defenses of hosts. The new analysis showed no evidence of such competition among HPV types, however. Instead, the diversity of HPV types may stem from recurring infections of particular types within individuals. While relatively few people are infected with any one type, the high overall HPV prevalence occurs because nearly half the adult population carries at least one type of genital HPV. The high risk of reinfection may be due to either auto-inoculation, spreading the infection by repeated contact between different sites on the body, or reactivation of a latent virus.”
According to lead author, Sylvia Ranjeva, a PhD student in the University of Chicago Department of Ecology and Evolution and the Pritzker School of Medicine, what makes this a “biologically significant result,” is that the men are not reacquiring the virus from a new partner. She added, “the best thing we can do is prevent the initial infection by vaccinating boys before sexual contact. However, if the increased risk of reinfection is due to auto-inoculation, then another effective strategy may be to vaccinate previously infected men as well.”